A survey by the financial information service Moneyfacts indicates that at least 10% of credit cards have raised their interest rates or fees.
As a result, the average rate on all cards has risen from 16.8% to 17.2% since the start of August.
Moneyfacts said card firms were giving themselves a cushion against defaults.
"During the past year, card companies have continued to increase the charges on their cards and consumers will find they will be stung more severely than ever before," said Michelle Slade of Moneyfacts.
"Just like on mortgages, card companies are factoring in a much bigger margin for the risk of consumers defaulting, so rates are going up rather than down," she added.
On Tuesday, Prime Minister Gordon Brown urged credit card providers to lend more responsibly and invited the industry to talks about establishing "clear and fair" principles for lending to the public.
A Downing Street spokesman said Mr Brown had been alarmed by some recent examples of very large and sudden increases in credit card charges.
Problem?
There are currently 163 credit cards on the market, said Moneyfacts, and since 1 August, increases in charges have included:
- 16 raising interest rates for purchases
- 12 raising rates for taking out cash
- 11 raising rates for transferring debts from other cards
- Seven increasing fees for borrowing cash
- Seven cutting the number of interest free days
- Four increasing fees for using cards abroad
The recent trend for credit cards to become more expensive started in April, with a variety of rate increases and higher fees being introduced.
The banking industry body, Apacs, denied that borrowing on cards was a general problem.
"If customers are borrowing on their cards and the majority don't, there are no indications from the Bank of England's most recent figures that a large number are undergoing difficulties in repaying those commitments," said a spokeswoman.
"In fact, these figures show that spending is lower and repayments on credit cards are higher than they were three years ago."
